A structure is described in FIG. 2 of WO01/036235 (PCT Japanese Translation Patent Publication No. 2003-525797), in which a retractor is arranged on a vehicle floor and the end of an inflatable lap belt is retracted around the retractor. In this conventional example, an inflator is arranged on the vehicle floor and a gas is introduced to the lap belt via a special structure called a plenum.
[Patent Document 1] PCT Japanese Translation Patent Publication No. 2003-525797
In the above-mentioned PCT Japanese Translation Patent Publication No. 2003-525797, the special member called the plenum is used so as to have a complicated structure and high cost. The plenum is also bulky and the degree of freedom in arrangement is low.